This invention relates to inertial sensors, and in particular to accelerometers and vibratory gyroscopes.
Vibratory gyroscopes provide a measure of an angular rate impressed on a vibrating element by producing a signal representative of torques on the vibratory element due to the impressed angular rate.
In the prior art, vibratory gyroscopes and accelerometers use a tuning fork, vibrating beam, or wire, as the vibrating element. However, the prior art gyroscopes and accelerometers have not proven to be easily adapted to miniaturization, or mass production.
It is known in the prior art to construct a vibrating beam accelerometer, comprising a resonant piezoelectric beam, which is sensitive to acceleration along the vibrating longitudinal axis of the beam. Acceleration along the axis shifts the resonant frequency, and the frequency shift is taken as a measure of the acceleration. Also known are vibrating string accelerometers, operative along a similar principal, in which the resonant member is a vibrating wire under tension. Acceleration along the axis of the wire relieves the tension, which again shifts the natural resonant frequency. Appropriate instrumentation converts the frequency shift to a measure of acceleration.
It has also been proposed to construct an accelerometer or seismometer by forming a micromechanical structure having a weight disposed on a elastic membrane or a pair of opposing elastic beams, as in United Kingdom patent application No. 2,130,373 published May 31, 1984. In that device, displacement of the weight manifests the acceleration along the direction of displacement.
Each of the foregoing constructions results in an instrument, the basic mechanical portion of which is simple. However, most such designs entail structures or adaptive circuitry which is not easily amenable to micro-miniaturization and mass production in a unitary chip form.
It is an object of this invention to provide an inertial sensor adapted for small geometry configurations.
Another object is to provide an inertial sensor which may be easily constructed, using mass production techniques.
Another object is to provide a novel structure for a sensor for providing a manifestation of the acceleration along an axis.
Another object is to provide a sensor having a digital output which is directly proportional to, or a known function of, the acceleration along an axis.
Another object is to provide a sensor having improved resolution.
Another object is to provide a sensor in the form of a micromechanical device.
Another object is to provide a sensor having integrally fabricated driving and sensing circuitry thereon.
Another object is to provide a sensor adaptable for directly integrating the sensed acceleration and providing a digital output indicative thereof.